The present invention relates to a drive control apparatus for a machine tool which rotates a workpiece about a predetermined axis and moves at least one of the workpiece and a tool for machining the workpiece so as to machine the workpiece into a desirable form.
Known as a drive control apparatus for the machine tool of this kind is one disclosed in Japanese Patent Application Laid-Open No. HEI 3-296109, for example. The drive control apparatus disclosed in Japanese Patent application Laid-Open No. HEI 3-296109 is one in which the drive control for a machine tool conventionally controlled by a cam, which is a mechanical element, is made electronic; and comprises a pulse encoder attached to a rotary object, rotary position storage means for reading out pulse signals outputted from the pulse encoder and storing rotary position data at each point in time, and command position storage means for storing command position data of a mobile axis set in response to each unit rotational position of the rotary object. As a consequence, the drive control apparatus generates movement command data on the mobile axis at each point in time from the above-mentioned rotary position data and command position data, and generates command speed data on the mobile axis synchronous to the rotational speed of the rotary object from the movement command data and the rotary position data, thereby controlling the position of a tool according to thus generated movement command data and command speed data.
Also known as a drive control apparatus for a similar machine tool is one disclosed in Japanese Patent Application Laid-Open No. HEI 5-189018, for example. The drive control apparatus for a machine tool disclosed in Japanese Patent Application Laid-Open No. HEI 5-189018 comprises cam phase arithmetic means for calculating a cam phase of a cam shaft at a given time, adjustment phase adding means for adding an adjustment phase to the cam phase so as to determine an adjusted cam phase, a cam curve memory for storing a cam curve, position reference means for calculating an axis position corresponding to the adjusted cam phase by referring to the cam curve memory, movement ratio multiplying means for multiplying the axis position by a movement ratio so as to determine a proportioned position, and adjustment movement quantity adding means for adding an adjustment movement quantity to the proportioned position so as to determine a final command position. As a consequence, the drive control means controls the position of a tool according to the final command position determined by the adjustment movement quantity adding means.
In a drive control apparatus such as the one disclosed in Japanese Patent Application Laid-Open No. HEI 3-296109, however, it is necessary for a memory such as RAM acting as the command position storage means to store the respective command position data of the mobile axis set so as to correspond to the individual unit rotational positions, i.e., all of a lot of position data concerning a desirable machining form, which increases the storage capacity of the memory. Also, for improving the accuracy in machining of the workpiece with the tool, it is necessary to finely set the above-mentioned unit rotational position so as to further enhance the number of position data, which greatly increases the storage capacity as well.
In a drive control apparatus such as the one disclosed in Japanese Patent Application Laid-Open No. HEI 5-189018, on the other hand, the cam position (radius) indicative of the form of the cam as a mechanical element is simply stored as a table of the cam phase and cam position into a memory (cam curve memory). Therefore, it is necessary to carry out arithmetic operations for taking account of a link mechanism between the cam and the tool (bite), a length adjustment mechanism for the tool (bite), and the like, so as to determine the mobile position of the tool from the cam position (radius) stored in the memory (cam curve memory). Though cam phases are set at predetermined irregular intervals in the above-mentioned table, cam positions are determined by proportionally distributing the cam position corresponding to the (mxe2x88x921)-th cam phase and the cam position corresponding to the m-th cam phase between the (mxe2x88x921)-th cam phase and the m-th cam phase, whereby the moving speed of the tool cannot be changed between the (mxe2x88x921)-th cam phase and the m-th cam phase, which imposes a limit to increasing the accuracy in machining the workpiece with the tool.
In view of the points mentioned above, it is an object of the present invention to provide a drive control apparatus for a machine tool, which can improve the accuracy in machining the workpiece with the tool without increasing the storage capacity for position data.
In order to achieve the above-mentioned object, the present invention provides a drive control apparatus for a machine tool for machining a workpiece into a desirable form by rotating the workpiece about a predetermined axis and moving at least one of the workpiece and a tool for machining the workpiece; the apparatus comprising reference timing signal generating means for generating a reference timing signal at each predetermined rotational angle in the predetermined axis; reference timing signal count means for counting the number of occurrences of the reference timing signal; position data storage means for storing position data respectively set so as to correspond to a plurality of different count values of the number of occurrences, the position data indicating a mobile position of at least one of the workpiece and tool; moving speed characteristic storage means for storing a moving speed characteristic of at least one of the workpiece and tool between two points in the position data; and mobile position defining means for reading out, each time the number of occurrences of the reference timing signal counted by the reference timing signal count means reaches the count value, position data corresponding to the reached count data and a next count data to reach from the position data storage means, and a moving speed characteristic corresponding to a part between the reached count value and the next count value to reach from the moving speed characteristic storage means, dividing the part between the reached count value and the next count value to reach into predetermined timings, and defining a mobile position of at least one of the workpiece and tool at each of the divided timings according to the read-out position data and moving speed characteristic; wherein at least one of the workpiece and tool is moved according to the mobile position defined by the mobile position defining means.
The drive control apparatus for a machine tool in accordance with the present invention comprises reference timing signal generating means, reference timing signal count means, position data storage means, moving speed characteristic storage means, and mobile position defining means. In particular, each time the number of occurrences of the reference timing signal counted by the reference timing signal count means reaches a count value, the mobile position defining means reads out position data corresponding to the reached count value and the next count value to reach from the position data storage means, reads out a moving speed characteristic corresponding to the part between the reached count value and the next count value to reach from the moving speed characteristic storage means, and divides the part between the reached count value and the next count value to reach into predetermined timings, so as to define the mobile position of at least one of the workpiece and tool at each timing according to the read-out position data and moving speed characteristic. Therefore, taking the reached count value and next count value to reach as start and end points, respectively, the machining form corresponding to the part between the start and end points is approximated as a linear segment. Consequently, it is sufficient for the position data storage means to store position data corresponding to the above-mentioned start point (reached count value) and end point (next count value to reach), which makes it unnecessary to store all of a lot of position data concerning the machining form. As a result, the storage capacity for position data in the position data storage means can be cut down greatly.
The position data storage means stores position data indicative of the mobile position of at least one of the workpiece and tool. As a consequence, arithmetic operations for taking account of the link mechanism, length adjustment mechanism, and the like become unnecessary, whereby the mobile position of at least one of the workpiece and tool at each of the divided timings can be defined rapidly.
Further, in the drive control apparatus for a machine tool in accordance with the present invention, the machining form corresponding to the part between the start and end points is approximated as a linear segment, and the moving speed of at least one of the workpiece and tool in the linear segment is controlled according to the moving speed characteristic stored in the moving speed characteristic storage means. Therefore, when machining a portion corresponding to the part between the start point (reached count value) and the end point (next count value to reach) in the workpiece, the moving speed of at least one of the workpiece and tool can be changed appropriately according to the moving speed characteristic. As a result, the accuracy in machining the workpiece with the tool can be improved.
In view of the foregoing, the drive control apparatus for a machine tool in accordance with the present invention can realize a drive control apparatus for a machine tool, which can improve the accuracy in machining the workpiece with the tool without increasing the storage capacity for position data.
In the drive control apparatus for a machine tool in accordance with the present invention, the machine tool may comprise a drive motor section for moving at least one of the workpiece and tool, whereas the mobile position defining means may sequentially output the defined mobile position as command data to the drive motor section in response to rotation of the predetermined axis.
Even in the case where a fluctuation occurs in rotation of a predetermined axis, a mobile position defined in the state additionally taking account of the fluctuation in rotation will be outputted as command data to the drive motor section if the mobile position defining means sequentially outputs the defined mobile position as the command data to the drive motor section in response to the rotation of the predetermined axis. As a result, the accuracy in machining the workpiece with the tool can further be improved.
In the drive control apparatus for a machine tool in accordance with the present invention, the machine tool may comprise a drive motor section for moving at least one of the workpiece and tool, whereas the mobile position defining means may sequentially output the defined mobile position as command data to the drive motor section at divided timings.
When the mobile position defining means sequentially outputs the defined mobile position as command data to the drive motor section at divided timings, a configuration capable of outputting the defined mobile position as command data to the drive motor section can be realized in a quite simple fashion.
In the drive control apparatus for a machine tool in accordance with the present invention, the count value may be defined such that the position data set so as to correspond to the count value represents the mobile position at a position where a machining form is changed such as a point of inflexion, a corner part, and a curvature changing point in the desirable form.
When the count value is defined such that the position data set so as to correspond to the count value represents the mobile position at a position where a machining form is changed such as a point of inflexion, a corner part, and a curvature changing point in the desirable form, the linear part in the machining form of the workpiece is restrained from being divided, whereby a position where a machining form is changed such as a point of inflexion, a corner part, and a curvature changing point in the desirable form is set as a start or end point. As a result, the storage capacity for position data in the position data storage means can be cut down more greatly.
In the drive control apparatus for a machine tool in accordance with the present invention, the count value may be defined so as to represent the mobile position at a dividing position where a curved part in the desirable form is divided.
When the count value is defined so as to represent the mobile position at a dividing position where a curved part in the desirable form is divided, the machining form corresponding to the part between the start and end points can be approximated as a linear segment even if a curved part exists in the machining form of the workpiece. As a result, the workpiece can be machined favorably even in the curved part without sacrificing the machining accuracy.
In the drive control apparatus for a machine tool in accordance with the present invention, the moving speed characteristic may be set so as to decelerate the moving speed of at least one of the workpiece and tool near a trailing end of the moving speed characteristic.
When the moving speed characteristic is set so as to decelerate the moving speed of at least one of the workpiece and tool near the trailing end of the moving speed characteristic, the moving speed is decelerated near a position corresponding to the end point in the machining form, whereby machining with a favorable accuracy can be carried out while continuing the machining. As a result, the machining time can be restrained from increasing.